The effects lasted for at least 3 months after treatment, making rTMS of the SMA a "good candidate as an add-on therapy" for patients with PD, say lead researcher Yuichiro Shirota (The University of Tokyo, Japan) and colleagues.

The benefit was also seen over and above the placebo response to rTMS. The researchers stress the importance of having a "realistic" sham rTMS treatment, which reproduces the sensation on the skin and also the clicking sound of genuine treatment. By week 9, which was 1 week after the conclusion of the 8-week treatment period, sham treatment of 34 patients produced an average 4.03-point improvement in the primary endpoint of change on the Unified Parkinson's Disease Rating Scale (UPDRS) part III.

The 34 patients given low-frequency (1 Hz) rTMS had a 4.91-point improvement in the primary endpoint and the 34 given high-frequency (10 Hz) rTMS had a 4.71-point improvement. The were no significant differences between the groups, which the team attributes to a "substantial sham effect" concealing the true benefits of treatment.

The effect of sham treatment had largely disappeared by 20 weeks after treatment, with these patients' UPDRS part III scores improved by an average of 2.71 points relative to baseline. By contrast, the average score in patients given low-frequency rTMS was 6.84 points improved from baseline, and this change was significantly better than that in the sham rTMS group. There were no improvements in nonmotor symptoms, apathy, or depression, however.

At week 20, the average UPDRS part III score in patients given high-frequency rTMS was just 0.71 points lower than at baseline. "Because the time course of change in UPDRS part III score was similar to that in the sham group, the transient improvement was likely caused by a nonspecific, placebo-like effect," write Shirota et al in Neurology.

They note that low- and high-frequency rTMS are thought to work by suppressing and stimulating brain activity, respectively. The benefits of low-frequency stimulation of the SMA are therefore in line with the benefits of deep-brain stimulation of the subthalamic nucleus, which also appears to result in reduced activity in the SMA.